We do not use Discord. Our middleman do not use Discord. All Trade Guardian services are on Epicnpc, NEVER off-site or via email. We do not investigate Discord disputes. Please contact members on our website.
The payment goes from buyer to seller directly, so the payment method entirely depends on your agreement with your seller.
As for the MM fee, you can pay using a credit card, bitcoin or through Amazon Pay. The MM could also pay the fee, which makes it possible for you to send a payment to the MM directly using a different payment method such as Paypal and he would cover the fee for you.